Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2001-07-11
2002-06-25
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06410771
ABSTRACT:
The present invention relates to a process for preparing trialkoxysilanes by reaction of silicon metal with an alcohol over fluorinated copper salts as catalysts, and to the use of fluorinated copper salts as catalysts in a process for preparing trialkoxysilanes.
Trialkoxysilanes, made up of a silicon atom to which three alkoxy groups and one hydrogen atoms are bound, are very reactive and unstable. They therefore undergo numerous reactions such as additions, copolymerizations, copolycondensations and disproportionation reactions with other organic compounds, giving a series of very useful substances. These are in turn employed as starting materials for silane coupling reagents, coating compositions, heat-resistant surface coatings or for obtaining high-purity monosilanes for semiconductor applications.
Trialkoxysilanes can be prepared by direct reaction of silicon metal with the corresponding alcohols at from 150 to 500° C. in the presence of copper-containing catalysts (direct synthesis). Here, the copper-containing silicon contact composition is generally suspended in an inert, liquid reaction medium and converted into the desired trialkoxysilanes at from 150 to 300° C. by introducing liquid or gaseous alcohol. In terms of the conversion of silicon metal and the selectivity to the trialkoxysilane relative to the tetraalkoxysilane formed as by-product, copper(I) chloride has been found to be a particularly suitable catalyst.
M. Okamoto et al., Catalysis Lett. 1995, 33, 421 to 427, reports a study of the reaction of silicon metal with methanol over various copper catalysts in a reactor containing a fixed silicon bed. The copper catalysts copper(I) oxide, copper(II) oxide, copper(II) acetate, copper(II) formate, copper(II) phthalate, copper(II) oxalate and copper(I) chloride were compared. Copper(I) chloride gave the highest silicon conversions (88%) and selectivities to trimethoxysilane relative to tetramethoxysilane (98%).
However, the use of copper(I) chloride results in formation of hydrochloric acid which makes it necessary to use expensive, corrosion-resistant materials for the reactors employed. Furthermore, the presence of chloride in the reaction mixture and the product leads to a reduction in the yield of trialkoxysilane, since the subsequent reaction of trialkoxysilane with alcohols to give tetraalkoxysilane is catalyzed by chloride. The hydrochloric acid formed when using copper(I) chloride as catalyst can, when methanol is used as alcohol, react with the methanol to form methyl chloride and water, so that methanol is lost as starting material for the trialkoxysilane synthesis.
For these reasons, the use of catalysts which do not contain any hydrolyzable halide is desirable.
JP-A-05170773 describes the preparation of trialkoxysilanes by reaction of silicon metal with alcohol in the presence of copper alkoxides. This reaction gives halide-free products. The selectivity of the reaction is from 91 to 92%, but the conversion of silicon is only from 21 to 32.4%.
An increase in the selectivity and the silicon conversion of this reaction is achieved according to JP-A-06065257 by use of a copper alkoxide catalyst in combination with a metal halide. However, the presence of halide in the reaction mixture and in the reaction product has the abovementioned disadvantages.
EP-A-0285133 relates to the preparation of trialkoxysilanes by reaction of silicon metal with alcohols using a copper(II) hydroxide catalyst. In this reaction, silicon conversions of from about 80 to 90 mol % are achieved and the proportion of tetraalkoxysilanes in the reaction mixture is from about 5 to 10 mol %, based on the silicon.
JP-A-10168084 relates to the preparation of trialkoxysilanes by reaction with silicon metal and alcohol over a copper(II) oxide catalyst having a water content of <3000 ppm. In the preparation of triethoxysilane, a selectivity coefficient for trialkoxysilane of 85.2 mol % and a silicon conversion of 91% by weight are achieved. However, the low water content of the catalyst used can require thermal pretreatment of the catalyst and thus an additional reaction step.
EP-A 0 517 398 discloses a process for preparing alkoxysilanes of the formula (OR)
n
SiH
4−n
, where n=2, 3 or 4, by reacting silicon with a solution of hydrogen fluoride or a salt which can be hydrolyzed to form hydrogen fluoride in a liquid primary or secondary alcohol, with or without addition of a copper catalyst. However, the use of hydrogen fluoride is problematical, since hydrogen fluoride is extremely toxic and attacks glass. Furthermore, the actual reaction has to be preceded by a pretreatment step in this process, since CuF
2
itself is inactive as catalyst.
It is an object of the present invention to provide a copper catalyst for the synthesis of trialkoxysilanes, which makes it possible to achieve a high selectivity to trialkoxysilane relative to tetraalkoxysilane and high conversions without the presence of hydrolyzable halide being necessary. No time-consuming preactivation for generation of a catalytically active species should be required.
The achievement of this object starts out from a process for preparing trialkoxysilanes by reaction of silicon metal with an alcohol in an inert solvent in the presence of a copper catalyst.
In the process of the present invention, the copper catalyst used is a copper salt whose anion contains at least one nonhydrolyzable fluorine atom, or a mixture thereof with other salts.
Preferred anions containing nonhydrolyzable fluorine atoms are selected from among fluoro complexes of carbon, sulfur, phosphorus and boron. Particular preference is given to trifluoroacetate, trifluorosulfonate, hexafluorophosphate and tetrafluoroborate. Very particular preference is given to trifluoroacetate, trifluorosulfonate and tetrafluoroborate.
Preference is given to using the copper(II) salts of the anions containing nonhydrolyzable fluorine atoms.
The problem of corrosion of the apparatuses used is significantly reduced compared to the use of copper chlorides as catalysts. Since the copper salts used contain only nonhydrolyzable fluoride, glass apparatuses can be used without the risk of the glass being attacked.
The reaction product of the reaction according to the present invention, namely trialkoxysilane is significantly stabilized against further reaction to form tetraalkoxysilane, in contrast to reaction products produced using copper chlorides.
The copper salts of anions containing nonhydrolyzable fluorine atoms which are used according to the present invention are commercially available. They can be obtained, for example, by reacting copper salts such as Cu(OH)
2
with the appropriate acids, e.g. trifluoroacetic acid, trifluorosulfonic acid, hexafluorophosphoric acid, tetrafluorophosphoric acid or tetrafluoroboric acid.
High silicon conversions and very good selectivities to trialkoxysilane relative to tetraalkoxysilane are achieved by means of the process of the present invention. In general, silicon conversions at the end of the reaction of >75 mol % are achieved, preferably from 80 to 90 mol %, particularly preferably from 82 to 90 mol %. Here, the silicon conversion is determined according to the following equation: Si[mol] in the product/amount of silicon used*100.
The selectivity to trialkoxysilane relative to tetraalkoxysilane is generally greater than 80 mol %, preferably from 85 to 95 mol %. Here, the selectivity is determined according to the following equation: trialkoxysilane[mol]/trialkoxysilane[mol]+tetraalkoxysilane[mol])* 100. Activation of the catalyst used according to the present invention by reduction or by means of a thermal treatment at high temperatures is not necessary.
In a further embodiment of the process of the present invention, further salts are used in addition to the copper salts whose anions contain nonhydrolyzable fluorine atoms which are used according to the present invention. These additional salts can be salts which are themselves catalytically active or can be additives for impr
BASF - Aktiengesellschaft
Keil & Weinkauf
Shaver Paul F.
LandOfFree
Fluorinated copper salts as catalysts for the synthesis of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fluorinated copper salts as catalysts for the synthesis of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fluorinated copper salts as catalysts for the synthesis of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2945214